The present invention relates to a sweeping unit for mounting on a carrier vehicle or on a trailer, comprising a carrying frame and at least one motor-driven rotary brush mounted in said carrying frame such that it can be rotated about its longitudinal axis, the carrying frame having supporting wheels, of which the vertical distance from the axis of the rotary brush can be changed by means of an adjusting unit, which comprises at least one adjusting element and a control apparatus.
Various designs of sweeping units of the type specified above are known, for example from European Patent 0372258 and German Offenlegungsschrift 3740215. Also known are sweeping units which have a construction essentially of the generic type, but differ therefrom in that the adjusting element, rather than being set via control apparatus, is part of a hydraulic regulating circuit, and in that, furthermore, the carrying frame does not have supporting wheels; such sweeping units can be gathered, for example, from German Offenlegungsschriften 2455200 and 2821627 and European Patent Applications 0189371 and 0843047.
For all the sweeping units known from the publications specified above, the correct setting of the sweeping-level width is extremely important for an efficient sweeping operation which, at the same time, does not adversely affect the materials. Thus, as is explained in detail in European Patent 0372258, the optimum sweeping-level width is characterized by a good cleaning result with a low level of bristle wear. If the sweeping-level width is below the optimum value, the cleaning capacity can noticeably decrease. With a sweeping-level width above the optimum value, in contrast, the bristle wear noticeably increases without any notable improvement to the cleaning result.
In order for the sweeping-level width to be set to its optimum value for the purposes explained above, it is necessary, inter alia, for the rotary brush to be adjusted in accordance with the bristle wear, i.e. for the distance between the axis of the rotary brush and the surface which is to be cleaned to be reduced gradually in accordance with the bristle wear. For this purpose, German Offenlegungsschriften 2455200 and 2821627 and European Patent Application 0843047 propose that the control apparatus of the adjusting unit acts on the adjusting element such that the driving torque for the rotary brush is always constant. According to German Offenlegungsschrift 3740215 and European Patent 0372258, on the other hand, the current diameter of the rotary brush (said diameter being dependent on the bristle wear) is measured by means of sensors and, in dependence on this measured value, the optimum distance between the axis of the rotary brush and the surface which is to be cleaned is determined and set. Finally, a time control means, in the case of which the running performance of the respective rotary brush, said performance being determined by an elapsed time meter, is evaluated as an indicator of the wear of said rotary brush and thus as a measure of the necessary adjustment, is known. None of the methods here is free of disadvantages. The sensing of the current diameter of the rotary brush by means of sensors requires a complicated measuring-sensor arrangement, which does not permanently withstand the harsh winter-service operations. Furthermore, the sensing element may ice up in unfavorable weather conditions and, consequently, indicates a rotary-brush diameter which is larger than the actual diameter. This results in an unsatisfactory cleaning result because the rotary brush is operated at too large a distance from the ground. The most serious disadvantage of the methods based on a constant driving torque is that the set sweeping-level width depends to an undesirable extent on the surface conditions, in particular the surface roughness; this means that, for example with surfaces made of concrete, a smaller sweeping-level width is set, on account of the greater friction, than for surfaces made of asphalt. Correspondingly, firmly adhering dirt such as loam and the like undesirably reduce the sweeping-level width, on account of the pronounced braking torque to which the rotary brush is subjected, as a result of which the cleaning result is adversely affected. The time control of the adjustment movement, since it only takes account of average wear conditions rather than the actual bristle wear which is dependent on the individual use conditions, is relatively imprecise.
Against the backdrop of the prior-art disadvantages explained above, the object of the present invention is to provide a sweeping unit of the generic type in which the optimum sweeping level can be set precisely with the lowest possible outlay, the intention being, furthermore, for the sweeping unit to be distinguished by a robust construction which is not susceptible to malfunctioning.
This object is achieved according to the present invention in that there is provided a sensor which senses the driving torque or the driving power of the rotary brush, or a variable linked thereto, and of which the signal is switched to the control apparatus, the control apparatus determining the operating position of the adjusting element, said operating position corresponding to the optimum sweeping-level width, as a function of the ground-contact position of the adjusting element, said ground-contact position being characterized, during lowering of the rotary brush, by an abrupt rise of the sensor signal.
In the sweeping unit according to the invention, the actual rotary-brush diameter, which is dependent on the bristle wear, is automatically taken into account for setting the position of said rotary brush relative to the surface which is to be cleaned, in that during the individual sweeping operation, the ground contact of the rotary brush and the corresponding ground-contact position of the adjusting element are used as reference points for the operating position of the adjusting element, said operating position corresponding to the optimum sweeping-level width. The ground contact of the rotary brush, during lowering of the latter, is determined here by an abrupt rise of the sensor signal which is emitted by a sensor which senses the driving torque or the driving power of the rotary brush or a variable linked thereto.
Problems of the type explained above in conjunction with the prior art do not arise in a sweeping unit according to the present invention. The sweeping-level width set by the control apparatus is not dependent on the surface conditions, in particular the roughness of the surface which is to be cleaned, nor is a complicated measuring-sensor arrangement which is susceptible to malfunctioning necessary. Nevertheless, the setting of the sweeping-level width is based not on an average degree of rotary-brush wear, which is dependent on the running performance of the relevant rotary brush, but on the actual degree of wear. Consequently, the present invention provides a sweeping unit in which the optimum sweeping level can automatically be set precisely with extremely low outlay on apparatus, the sweeping unit, furthermore, being distinguished by a robust construction which is not susceptible to malfunctioning.
The present invention can advantageously be used if the operating position of the adjusting element is determined, in the control apparatus, from the ground-contact position of the adjusting element by the addition of a constant variable. In this case, in other words, the rotary brush, during the sweeping operation, would be lowered in each case into a position which is located a certain distance (e.g. 2 mm) below the ground-contact position. Although, as a result of the geometrical relationships, this would result, with continuing wear of the rotary brush, in a gradual reduction in the sweeping-level width, it would be compensatedxe2x80x94at least partiallyxe2x80x94by an increasing hardness of the brush, so that the cleaning result would essentially stay the same.
In contrast, however, a preferred development of the present invention is distinguished in that the adjusting-element advancement movement, by means of which the operating position of the adjusting element differs from the ground-contact position thereof, is dependent on the actual diameter of the rotary brush. In this case, the control apparatus comprises a corresponding compensation circuit, for example in the form of a characteristic curve, which specifies the advancement movement, i.e. the difference between the operating position and ground-contact position of the adjusting element, in dependence on the actual diameter of the rotary brush. This actual diameter may be derived directly from the ground-contact position of the adjusting element sincexe2x80x94with supporting wheels resting on the surface which is to be cleanedxe2x80x94each diameter of the rotary brush has precisely one ground-contact position of the adjusting element corresponding to it. Other suitable measuring devices which are intended for determining the diameter of the rotary brush, and likewise evaluate the position of the rotary brush relative to the carrying frame in the ground-contact position of the rotary brush, can be used in the same way. These include, in particular, an angle-measuring instrument which determines the angular position of at least one carrying arm of the rotary brush relative to a further component of the carrying frame. The critical factor is that the diameter of the rotary brush, rather than being measured directlyxe2x80x94via sensorsxe2x80x94in each case, is derived from the position of the rotary brush at the moment at which it comes into contact with the ground, and thus indirectly utilizing the signal of the ground-contact sensor.
A preferred development of the sweeping unit according to the invention is distinguished in that the at least one adjusting element is designed as a hydraulic adjusting cylinder. In this case, there is particularly preferably hydraulically connected to the adjusting cylinder a supply cylinder, of which the hydraulic operating chamber, which communicates with the adjusting cylinder, has a smaller cross-sectional surface area than the at least one adjusting cylinder. The supply cylinder serves here for the volumetric proportioning of the hydraulic fluid to the at least one adjusting cylinder, this corresponding to the advancement movement of the adjusting cylinder from its ground-contact position into its operating position. A bypass line to the supply cylinder is particularly preferably provided since said supply cylinder is required merely for the precise lowering of the rotary brush from its ground-contact position into its operating position. There is no need for a volumetric determination of the hydraulic fluid volume which is fed to the at least one adjusting cylinder or flows out of the same, either during lowering of the rotary brush into its ground-contact position or during raising of the rotary brush, respectively. The abovementioned configuration of a hydraulic system with a supply cylinder results in it being possible for the at least one adjusting cylinder to be set particularly precisely.
Although it is conceivable, within the context of the abovementioned development of the present invention, for a mechanical adjusting drive to act on the piston of the supply cylinder, with the result that the supply cylinder itself performs the function of a pump, it is particularly preferable for the supply cylinder to be connected between a hydraulic pump and the at least one adjusting cylinder. It follows along in this case, the volume of the hydraulic fluid fed to the at least one adjusting cylinder being determined by the number of strokes of the supply cylinder and/orxe2x80x94in the case of incomplete strokesxe2x80x94by the displacement of the piston of the supply cylinder.